Titanium dioxide pigment and method for producing the same and resin composition using the same

ABSTRACT

The titanium dioxide pigment of the present invention contains an anatase type crystal in an amount of 98-100% and has an average particle diameter of 0.2-0.4 μm and a whiteness of 95-97 in terms of L value of linseed oil. The titanium dioxide pigment of the present invention has characteristics peculiar to anatase type, for example, optical characteristics such as bluish color tone and physical characteristics such as low hardness, and furthermore has high opacity which is not possessed by conventional anatase type titanium oxide pigments.

TECHNICAL FIELD

The present invention relates to an anatase type titanium dioxidepigment excellent in opacity, a method for production thereof, and aresin composition comprising the same.

BACKGROUND ART

Titanium dioxide is used as white pigments in a wide variety of thefields such as paints, inks, plastics and papers, and those which arecommercially available at present are roughly classified into anatasetype and rutile type according to their crystalline forms. Those ofanatase type have the features of higher reflectance for light of shortwavelength (showing bluish color tone), smaller absorption of light ofultraviolet portion, lower hardness, lower dielectric constant, andsmaller specific gravity as compared with those of rutile type, but areinferior in basic properties of pigments, namely, smaller in refractiveindex for visible light and lower in opacity than those of rutile type.Thus, the features of anatase type titanium dioxide are not sufficientlyutilized. The pigment concentration used in resin compositions whichrequire high opacity is usually not less than 0.5 part by weight oftitanium dioxide pigment for 1 part by weight of resin component in thecase of paints, inks or the like, and usually not less than 0.05 part byweight in the case of plastics or the like. Commercially availableanatase type titanium dioxide pigments have an average particle diameterin the range of 0.1-0.18 μm, and the reason for the anatase typetitanium dioxide pigments being low in opacity is that the particlediameter is too small as compared with optimum particle diameter whichcan give theoretically the highest opacity, although the reason might bedue to the basic property that anatase type titanium dioxide pigmentsare low in refractive index for visible light as mentioned above.

As a method for producing anatase type titanium dioxide pigments havingan average particle diameter of not less than 0.2 μm, there is known amethod which comprises adding to hydrous titanium oxide a potassiumoxide corresponding to 0.2-0.6% by weight calculated as K₂O based on theweight of TiO₂ in the hydrous titanium oxide and a phosphorus oxidecorresponding to 0.15-0.55% by weight calculated as P₂O₅ as calcinationtreating agents, preferably further adding an aluminum compound in anamount of not less than 0.2% by weight calculated as Al₂O₃, andcalcining the mixture with heating by gradually raising the temperaturefrom 460° C. to 1020° C. over a certain period of time(J-P-A-8-225-324). Furthermore, there is known another method whichcomprises adding to hydrous titanium oxide an aluminum compoundcorresponding to 0.1-0.5% by weight calculated as Al₂O₃, a potassiumcompound corresponding to 0.1-0.7% by weight calculated as K₂O and aphosphorus compound corresponding to 0.2-1% by weight calculated as P₂O₅based on the weight of TiO₂ in the hydrous titanium oxide as calcinationtreating agents, and calcining the mixture by heating at 1000° C. orhigher (JP-A-9-188518).

DISCLOSURE OF INVENTION

However, according to the method of JP-A-8-225324, sufficient whitenessas white pigments cannot be obtained, and according to the method ofJP-A-9-188518, since the calcination temperature is high, and a part ofcrystals of anatase type titanium dioxide is converted to rutile typeduring the calcination with heating, the resulting pigment containsabout 2-8% by weight of rutile type titanium dioxide, and hence thefeatures of anatase type can hardly be obtained, and, furthermore,sintering is apt to occur between particles, and titanium dioxidepigments excellent in dispersibility can hardly be obtained. The presentinvention solves the above-mentioned problems and provides anatase typetitanium dioxide pigments excellent in opacity, a method for producingthe pigments, and a resin composition comprising the same.

As a result of intensive research conducted by the inventors in anattempt to solve the above problems, it has been found that when analuminum compound, a potassium compound and a phosphorus compound areused as calcination treating agents, and amounts of these compounds andthe ratio of the potassium compound and the phosphorus compound are inspecific ranges, anatase type titanium dioxide pigments great inparticle diameter and excellent in whiteness can be obtained at acalcination temperature lower than 1000° C. It has further been foundthat when the resulting titanium dioxide pigments are used in resincompositions, the compositions show excellent opacity and havecharacteristics of anatase type which are not possessed by rutile typetitanium dioxide pigments. Thus, the present invention has beenaccomplished.

That is, the present invention includes (1) a titanium dioxide pigment,characterized in that it contains an anatase type crystal in an amountof 98-100% and has an average particle diameter in the range of 0.2-0.4μm and a whiteness in the range of 95-97 in terms of L value of linseedoil, (2) a method for producing an anatase type titanium dioxide pigmentby calcination of hydrous titanium oxide with heating, characterized inthat an aluminum compound corresponding to 0.02-0.2% by weightcalculated as Al₂O₃, a potassium compound corresponding to 0.2-1% byweight calculated as K₂O and a phosphorus compound corresponding to0.02-0.5% by weight calculated as P₂O₅ based on the weight of TiO₂ inthe hydrous titanium oxide with K₂O/P₂O₅ being in the range of1.5/1-10/1 are used as calcination treating agents, and the hydroustitanium oxide is calcined by heating at a temperature of not lower than800° C. and lower than 1000° C. in the presence of the above calcinationtreating agents, and (3) a resin composition comprising the abovetitanium dioxide pigment.

The titanium dioxide pigment of the present invention hascharacteristics peculiar to anatase type, for example, opticalcharacteristics such as bluish color tone and physical characteristicssuch as low hardness, and furthermore has high opacity not possessed bythe conventional anatase type titanium oxide pigments, and hence isuseful in various resin compositions, particularly, those which containresins for paints, inks, plastics or the like.

BEST MODE FOR CARRYING OUT THE INVENTION

The titanium dioxide pigment of the present invention is characterizedby containing an anatase type crystal in an amount of 98-100% and havingan average particle diameter in the range of 0.2-0.4 μm and a whitenessin the range of 95-97 in terms of L value of linseed oil. In the presentinvention, the average particle diameter is specified in theabove-mentioned range which is most suitable for the pigmentconcentration used in a resin composition which requires high opacity(e.g., not less than 0.5 part by weight of titanium dioxide pigment for1 part by weight of resin component in the case of paints, inks or thelike, and not less than 0.05 part by weight of titanium dioxide pigmentin the case of plastics or the like), whereby excellent opacity isimparted to an anatase type titanium dioxide pigment which is inherentlylow in refractive index. The titanium dioxide pigment of the presentinvention has a whiteness of 95-97 expressed by L value of linseed oil.Furthermore, in the field of plastics in which shear force is hardlyexerted at the time of processing, dispersion of titanium dioxidepigment is more difficult with increase of the pigment concentration ascompared with paints and inks, while the titanium dioxide pigment of thepresent invention is large in particle diameter and small in surfaceenergy, and hence is superior in dispersibility.

If the content of the anatase type crystal is lower than the aboverange, it becomes difficult to develop the features of anatase typetitanium dioxide, such as bluish color tone, absorptive power forultraviolet portion, hardness, etc. If the average particle diameter issmaller than the above range, not only the desired effects cannot beobtained, but also the surface energy increases to cause deteriorationof dispersibility. Even if the average particle diameter is increased tolarger than the above range, further improvement of the opacity is notrecognized, and rather reflectance for light of short wavelength whichis one of the features of anatase type decreases, resulting in yellowishcolor tone. More preferred range of average particle diameter is 0.2-0.3μm. Particularly, when the width of particle size distribution isnarrow, the desired effects can be readily obtained, and in the presentinvention, it is especially preferred that particles having a particlediameter in the range of 0.2-0.4 μm are contained in 50-100% by weight,more preferably 60-100 wt %. In the present invention, content of rutiletype crystal (R(%)) is obtained by X-ray diffraction, and 100-R (%) istaken as a content of anatase type titanium dioxide. Furthermore, theaverage particle diameter is a cumulative 50% particle diameter ofprimary particles which is measured by electron microscopy, and theprimary particles mean particles of minimum unit which are hardlydisintegrated by mechanical methods which are often industriallyemployed.

The surface of the titanium dioxide pigment of the present invention maynot be coated, but is preferably coated with some inorganic compoundsince anatase type titanium dioxide is high in photocatalytic activityand low in light resistance and weathering resistance. Furthermore,since titanium dioxide pigment is hydrophilic, it is preferably furthercoated with an organic compound in order to impart a high affinity forthe resin component.

As the inorganic compounds which can be used for coating the surface ofthe titanium dioxide pigment of the present invention, mention may bemade of, for example, aluminum compounds, silicon compounds, zirconiumcompounds, tin compounds, titanium compounds, antimony compounds, etc.One of these compounds may be coated or two or more of them may becoated in combination by coating them in the form of laminate or as amixture of them. More preferably, the inorganic compounds are at leastone compound selected from oxides, hydroxides, hydrated oxides, andphosphate salts. It is known that the coating layer of the inorganiccompounds can be made porous or dense by controlling the conditions ofcoating treatment, such as pH and temperature, and the state of thecoating layer is also not particularly limited in the present invention.The coating amount of the inorganic compound is about 0.05-15% byweight, although it depends on use of the resin composition and kind ofthe inorganic compound. More preferably, it is 0.1-15% by weight in thecase of titanium dioxide pigment used for paint compositions or inkcompositions and 0.05-5% by weight in the case of titanium dioxidepigment used for plastics compositions. The above coating amount isexpressed in terms of oxide in the case of oxides, hydroxides andhydrated oxides (e.g., calculated as Al₂O₃ in the case of hydroxide ofaluminum), and in terms of phosphate in the case of phosphate salts(e.g., calculated as AlPO₄ in the case of aluminum phosphate).

The inorganic compounds used for coating of surface are preferablycompounds of silicon, zirconium, tin or antimony, and desirably hydratedoxides thereof. The hydrated oxides of silicon are preferably coated inthe dense state from the viewpoint of weathering resistance. Thehydrated oxides of aluminum or titanium are known to have the effects toimpart an affinity for a resin composition and to improve operabilitysuch as dehydration, drying or grinding in production steps, and it ispreferred to coat at least the hydrated oxide of aluminum as the secondlayer (the outer layer) on the titanium dioxide pigment.

As the organic compounds which can be used for surface coating of thetitanium dioxide pigment of the present invention, mention may be madeof, for example, polyhydric alcohols, alkanolamines or derivativesthereof, organosilicon compounds, higher fatty acids or metal saltsthereof, etc. Examples thereof are trimethylolethane, tripropanolethane,pentaerythritol, etc. as the polyhydric alcohols; triethylamine, etc. asthe alkanolamines; polysiloxanes such as dimethylpolysiloxane andmethylhydrogenpolysiloxane, alkylsilanes such as hexyltrimethoxysilane,and organosilanes, e.g., silane coupling agents such as aminosilane,vinylsilane and phenylsilane as the organosilicon compounds; stearicacid, etc. as the higher fatty acids; and magnesium stearate, zincstearate, etc. as the metal salts of higher fatty acids. The kind,combination and coating order of these organic compounds can also beselected depending on the purpose. Total coating amount of the organiccompounds is preferably 0.01-5% by weight, more preferably 0.05-2% byweight.

A specific example of the composition of surface coating is a coatingcomprising a hydrated oxide of aluminum in an amount of 1-5% by weight,preferably 1-4% by weight calculated as Al₂O₃. This compound is superiorin dispersibility and is suitable for paints which require high gloss.Since anatase type titanium dioxide is high in photocatalytic activity,titanium dioxide pigment which has the coating layer of the abovehydrated oxide of aluminum as the second layer (the outer layer) and adense coating layer of a hydrated oxide of silicon in an amount of 1-10%by weight, preferably 1-5% by weight calculated as SiO₂ as the firstlayer of the outermost shell (coated on the surface of the titaniumdioxide pigment) is suitable for paints which require weatheringresistance. Furthermore, a hydrated oxide of zirconium in an amount of0.05-5% by weight, preferably 0.05-2% by weight calculated as ZrO₂ maybe coated in place of the hydrated oxide of silicon, and moreover ahydrated oxide of tin in an amount of 0.05-5% by weight, preferably0.05-2% by weight calculated as SnO₂ may be laminated on the coatinglayer of hydrated oxide of zirconium. When a polyhydric alcohol,preferably trimethylolethane or trimethylolpropane is coated in anamount of 0.1-2% by weight, preferably 0.1-1% by weight on the titaniumdioxide pigment coated with the inorganic compound, the affinity for theresin component of paints is further enhanced, which is preferred.

Another example is a titanium dioxide pigment which is coated with ahydrated oxide of silicon in an amount of 2-10% by weight, preferably2-6% by weight calculated as SiO₂ as the first layer (the inner layer)and a hydrated oxide of aluminum in an amount of 1-10% by weight,preferably 1-5% by weight calculated as Al₂O₃ as the second layer (theouter layer). This titanium dioxide pigment is high in opacity andexcellent in printability, particularly, for reverse printing gravureink or flexographic ink. It can be selected within the above-mentionedrange of coating amount whether the coating layer of the hydrated oxideof silicon should be a dense layer, a porous layer or a laminate layerof dense layer and porous layer. For flexographic ink, especiallypreferred is the titanium dioxide pigment coated with the hydratedoxides of silicon and aluminum in the above ranges wherein the totalcoating amount is in the range of 5-15% by weight. Alternatively, atitanium dioxide pigment coated with no hydrated oxide of silicon andcoated with only the hydrated oxide of aluminum in an amount of 5-15% byweight, preferably 5-10% by weight calculated as Al₂O₃ can also be usedfor flexographic inks. When a hydrated oxide of titanium in an amount of0.1-5% by weight, preferably 0.1-2% by weight calculated as TiO₂ iscoated in place of the silicon compound as the first layer (the innerlayer), the titanium dioxide pigment becomes high in gloss and issuitable for surface printing gravure inks. When a polyhydric alcohol,preferably trimethylolethane or trimethylolpropane is coated in anamount of 0.1-2% by weight, preferably 0.1-1% by weight on the titaniumdioxide pigment coated as mentioned above, the affinity for the resincomponent of inks is enhanced, which is preferred.

Further another example is a titanium dioxide pigment which is coatedwith a hydrated oxide of aluminum in an amount of 0.05-3% by weight,preferably 0.1-2% by weight calculated as Al₂O₃. When this is used as atitanium dioxide pigment for plastics, the photocatalytic activity isreduced to some extent and content of water originating from thehydrated oxide of aluminum is low, and, therefore, this is suitable forprocessing at high temperatures. Alternatively, when an aluminumphosphate hydrate in an amount of 0.1-5% by weight, preferably 0.5-3% byweight calculated as AlPO₄ is coated in place of the aluminum-compound,the titanium dioxide pigment is further improved in light resistance.When an organic compound is further coated in an amount of 0.1-2% byweight, preferably 0.1-1% by weight on the titanium dioxide pigmentcoated with the above inorganic compound, the affinity for the resincomponent is enhanced, which is more preferred. Preferred organiccompounds are polyhydric alcohols such as trimethylolethane andtrimethylolpropane, organosilicon compounds such as polysiloxanes,alkylsilanes and aminosilanes, and higher fatty acids such as stearicacid. Since organosilicon compounds and higher fatty acids render thesurface of titanium dioxide hydrophobic, not only a high affinity forthe resin component is obtained, but also water absorption isconsiderably inhibited. Moreover, they have an effect to inhibitdiscoloration of phenolic antioxidants such as BHT added to plastics.

Next, the present invention relates to a method for producing an anatasetype titanium dioxide pigment by calcination of a hydrous titanium oxidewith heating in the presence of a calcination treating agent, whichcomprises calcining the hydrous titanium oxide by heating it at atemperature of not lower than 800° C. and lower than 1000° C., using asthe calcination treating agents an aluminum compound corresponding to0.02-0.2% by weight calculated as Al₂O₃, a potassium compoundcorresponding to 0.2-1% by weight calculated as K₂O and a phosphoricacid compound corresponding to 0.02-0.5% by weight calculated as P₂O₅based on the weight of TiO₂ in the hydrous titanium oxide, the ratioK₂O/P₂O₅ being in the range of 1.5/1-10/1. It is considered that thepotassium compound and the phosphoric acid compound act synergisticallyto provide an effect to regulate the shape of the particles produced,and the aluminum compound has an action to inhibit occurrence of thephenomenon that titanium dioxide is reduced during calcination byheating to cause deterioration of whiteness. Therefore, in order toincrease the particle diameter by firing at high temperatures, there areneeded the potassium compound, the phosphoric acid compound and thealuminum compound in the amounts of the above ranges. On the other hand,if the amount of the phosphoric acid compound is too large, it issupposed that the compound hinders the growth of particles, and in orderto obtain large particles, calcination at the higher temperature isneeded, but since anatase type crystals have the property of beingreadily converted to rutile type at high temperatures, production ofrutile type cannot be inhibited. However, it is considered that in thepresent invention the ratio of the potassium compound and the phosphoricacid compound added is specified in the above range, and, as a result,the particles can be grown even at a temperature lower than 1000° C.,and the desired titanium dioxide pigment which has substantially anatasetype crystal and is large in particle diameter and excellent inwhiteness can be obtained.

Preferred ranges of the amount of the aluminum compound, the potassiumcompound and the phosphoric acid compound are 0.05-0.2% by weight (0.2is not inclusive), 0.2-0.5% by weight and 0.02-0.2% by weight (0.2 isnot inclusive), respectively, and preferred range of the ratio of thepotassium compound and the phosphoric acid compound is 2/1-10/1. In thepresent invention, aluminum oxide, aluminum chloride, etc. can be usedas the aluminum compound, potassium hydroxide, potassium chloride, etc.can be used as the potassium compound, and orthophosphoric acid,metaphosphoric acid, pyrophosphoric acid and salts thereof, etc. can beused as the phosphoric acid compound. The method of adding thesecalcination treating agents is not limited, and, for example, there is amethod of dispersing the hydrous titanium oxide in a dispersion mediumsuch as water and then adding the calcination treating agents to thedispersion, followed by mixing.

A hydrous titanium oxide is calcined by heating in the presence of theabove calcination treating agents to obtain an anatase type titaniumdioxide pigment having an average particle diameter of 0.2-0.4 μm. Thehydrous titanium oxide used in the present invention has an anatase typestructure and can be obtained by a method for the production of titaniumdioxide pigment, which is called sulfuric acid process. For example, atitanium-containing ore such as ilmenite ore or titanium slug which isground, if necessary, is dissolved in sulfuric acid, thereby reactingthe titanium component with sulfuric acid to produce titanyl sulfate(TiOSO₄), which is classified by allowing to stand, filtered and thenhydrolyzed with heating to obtain the desired hydrous titanium oxide.Alternatively, there may be applied a method of hydrolyzing the titanylsulfate in the presence of a previously prepared nucleus crystal. Thenucleus crystal is obtained, for example, by aging hydrous titaniumoxide. The particle diameter of the hydrous titanium oxide used ispreferably 0.001-0.01 μm. Furthermore, the amount of sulfate groupcontained in the hydrous titanium oxide is desirably at most 0.1% byweight calculated as SO₄. If the sulfate group is contained in an amountof more than 0.1% by weight, the anatase type titanium dioxide obtainedby calcination decreases in whiteness and cannot be used as pigment. Thecalcination temperature is more preferably 800-980° C. For calcinationby heating, there may be used known apparatuses such as rotary kiln andtunnel kiln.

After titanium dioxide particles of desired particle diameter areobtained, they may be subjected to wet grinding, dehydration

washing, drying and dry grinding by known methods. Moreover, between therespective steps, coating treatment with inorganic compound or organiccompound can be optionally carried out. A vertical sand mill, ahorizontal sand mill, etc. can be used for the wet grinding; a band typeheater, a batch type heater, etc. can be used for the drying; and shockgrinding machines such as a hammer mill and a pin mill, attritiongrinding machines such as a disintegration grinding machine, flashgrinding machines such as a jet mill and snail mill, and a spray dryingmachine can be used for dry grinding.

The coating with inorganic compound can be carried out in the followingmanner. That is, the titanium dioxide particles are dispersed in aliquid medium such as water to prepare a slurry. After the slurry ispreferably subjected to further wet grinding, a solution of a salt ofthe desired inorganic compound is added thereto, followed by adding anacidic compound or a basic compound, or a salt of the inorganic compoundand an acidic compound or a basic compound are simultaneously added tocarry out a neutralization reaction, thereby depositing the inorganiccompound on the surface of the titanium dioxide particles. The salts ofinorganic compounds which can be used in the present invention include,for example, sodium aluminate, aluminum sulfate and aluminum nitrate assalts of aluminum compound, sodium silicate and potassium silicate assalts of silicon compound, zirconium chloride as salts of zirconiumcompound, tin chloride as salts of tin compound, and titanium chlorideand titanium sulfate as salts of titanium compound. The acidic compoundsinclude, for example, inorganic acids such as sulfuric acid andhydrochloric acid, and organic acids such as acetic acid. The basiccompounds include, for example, hydroxides or carbonates of alkalimetals or alkaline earth metals such as sodium hydroxide, potassiumhydroxide and sodium carbonate, ammonium compounds such as ammonia, andamines.

When the titanium dioxide particles is coated with an organic compoundwhich does not bond to the surface of the titanium dioxide particles oris weak in bonding force, such as a polyhydric alcohol, an alkanolamineor a derivative thereof, a polysiloxne, or a higher fatty acid or aderivative thereof, the coating is preferably carried out by drygrinding the titanium dioxide particles and then mixing the titaniumdioxide particles with the organic compound by a high-speed stirrer suchas Henschel mixer or super mixer or by employing so-called dry treatmentwhich comprises charging the titanium dioxide particles and the organiccompound in a dry grinding machine to simultaneously carry out grinding,mixing and coating. The method of simultaneously carrying out grindingand coating by a flash grinding machine is industrially preferredbecause the organic compound is apt to be uniformly coated and, further,the treating performance is high. In the case of coating an organiccompound such as an organosilane which reacts with the surface of thetitanium dioxide particles to firmly bond to the surface, there can beemployed so-called wet treatment which comprises adding the organiccompound to a titanium dioxide slurry after wet grinding or aftercoating with inorganic compound. Moreover, there may be employed amethod which comprises subjecting the higher fatty acid salt such assodium stearate to neutralization treatment in the titanium dioxideslurry to form a coating layer of the higher fatty acid.

Further, the present invention provides a resin composition comprisingthe above titanium dioxide pigment and a resin component. Since theresin composition of the present invention contains the titanium dioxidepigment, it has high opacity in addition to the optical characteristicsand physical characteristics possessed by the conventional anatase typetitanium oxides. Moreover, according to the present invention, thetitanium dioxide pigment can be contained in a high concentration, andhence resin compositions useful for various uses such as paints, papersand fibers can be obtained by selecting the kind of the resin component.Particularly, the titanium dioxide pigment is useful for paintcompositions, ink compositions, and plastics compositions. The specificpigment concentration which varies depending on the use is preferably0.5-10 parts by weight of the titanium dioxide pigment based on 1 partby weight of the resin component in the case of paint compositions orink compositions, and 0.05-2 parts by weight based on 1 part by weightof the resin component in the case of plastics compositions. In thepresent invention, solvents, additives, fillers, etc. may be containedin addition to the titanium dioxide pigment and the resin component.

The resin composition of the present invention which contains a paintresin is not only high in opacity, but also is not needed to besubjected to toning with a color pigment and dye, a fluorescentbrightening agent, etc. due to the characteristics of anatase type,namely, high reflectance for light of short wavelength, whereby vividwhite color tone is obtained in the field which requires bluish colortone. When an ultraviolet-curing resin is used as the paint resin, theanatase type titanium dioxide can hardly absorb ultraviolet rays havinga wavelength near the visible light, and hence the curing is nothindered as is caused in the rutile type titanium dioxide. The resincomposition of the present invention which contains a paint resin can beused for painting of various base materials such as metals, woods,plastics, and concrete, and is particularly suitable for coating ofindoor members. The painting methods include various known methods suchas brushing, roller coating, spray coating, dip coating, electrostaticcoating, etc.

When a titanium dioxide pigment coated with a hydrated oxide of aluminumin an amount of 1-5% by weight, preferably 1-4% by weight calculated asAl₂O₃ is used as the titanium dioxide pigment contained in the resincomposition of the present invention containing a paint resin as a resincomponent, the resulting resin composition provides a coating filmexcellent in gloss. Moreover, when the above coating layer of thehydrated oxide of aluminum is provided as the second layer (the outerlayer), and a dense layer of a hydrated oxide of silicon in an amount of1-10% by weight, preferably 1-5% by weight calculated as SiO₂ isprovided as the first layer (the inner layer) (present in contact withthe surface of the titanium dioxide pigment), the resulting resincomposition gives a coating film excellent in weathering resistance.Furthermore, a hydrated oxide of zirconium in an amount of 0.05-5% byweight, preferably 0.05-2% by weight calculated as ZrO₂ may be coated inplace of the hydrated oxide of silicon, and furthermore a hydrated oxideof tin in an amount of 0.05-5% by weight, preferably 0.05-2% by weightcalculated as SnO₂ may be laminated on the coating layer of the hydratedoxide of zirconium. Moreover, when a polyhydric alcohol, preferablytrimethylolethane or trimethylolpropane is further coated in an amountof 0.1-2% by weight, preferably 0.1-1% by weight, the affinity for theresin component is enhanced, and not only the productivity of paint isimproved, but also a coating film higher in gloss can be provided.

The paint resin components include, for example, alkyd resins, acrylicresins, polyester resins, epoxy resins, amino resins,fluorine-containing resins, modified silicone resins, urethane resins,vinyl resins, etc. and they can be optionally selected. These paintresin components are of organic solvent-dissolving type, water-solubletype, emulsion type, etc., and are not particularly limited. Curingmethods are also not limited, and can be heat-curing type, cold-curingtype, ultraviolet-curing type, electron ray-curing type, etc. The resincomposition of the present invention containing the paint resin maycontain organic solvents such as alcohols, esters, ethers, ketones,aromatic hydrocarbons, and aliphatic hydrocarbons, water or mixedsolvents thereof as solvents, and the solvents are selected depending onsuitability for the resin components. In addition, there may becontained various additives, e.g., coloring agents such as organicpigments, inorganic pigments and dyes, extenders, surface active agents,plasticizers, curing aids, dryers, anti-foaming agents, thickeningagents, emulsifiers, flow adjusters, anti-skinning agents,anti-segregating agents, ultraviolet absorbers, and mildew-proofingagents, and fillers, etc. depending on the purpose. Furthermore, theresin composition may be in the form of a two-pack paint used by addingto the paint the curing agent, the curing aid and the curing resincomponent as a separate curing solution at the time of painting. It ispreferred to further add a photopolymerization initiator, a lightsensitizing agent, etc. to the resin composition containing theultraviolet curing type resin.

When a paint resin is used as the resin component, the resin compositionof the present invention is obtained by adding, if necessary, varioussolvents to the titanium dioxide pigment and the paint resin component,followed by dispersing them using a dispersing machine such as sandmill, disper, ball mill, paint shaker, twin-roll mill, or triple rollmill. The above additives and fillers can be added to the paint duringdispersing or after dispersing.

In case the resin composition of the present invention containing an inkresin is used especially for gravure printing inks such as reverseprinting inks and surface printing inks, abrasion of doctor blade isinhibited, printing defects such as fogging of plate and doctor lineshardly occur due to the characteristics of anatase type, namely, lowerhardness, and the opacity is excellent due to the characteristic ofanatase type titanium dioxide, namely, lower hardness. Moreover,recently, there are demanded speeding-up of printing and switching towater-soluble inks, non-toluene type inks and ultraviolet-curing typeinks which are less in environmental pollution, and in thesetechnologies, increase of drying speed is important. At p resent, as onesolution, investigation on reduction of coating film thickness is beingconducted, but if the film thickness is reduced, opacity equal to thatof the conventional technologies cannot be obtained, and if the pigmentconcentration is increased to enhance the opacity, the doctor blade isapt to be abraded. In the present invention, since the abrasion of thedoctor blade is inhibited as mentioned above, it is easy to increase thepigment concentration. Furthermore, the printing method using doctorblade also spreads in flexographic printing, and in this field,deterioration of productivity owing to changing of abraded doctor bladescauses problems, while when the present invention is employed, theintervals for exchanging of doctor blades can be prolonged. The resincomposition of the present invention containing an ink resin is usefulfor various printing inks used for intaglio printing, letterpressprinting, lithographic printing and stencil printing other than theabove-mentioned gravure printing and flexographic printing, and thesubstrates to be printed are not limited and include plastics, films,papers, metal foils, etc. Further, the present invention is applied tonot only the final printing inks, but also to intermediate articles suchas toning inks and color chips.

When a titanium dioxide pigment having a coating layer of a hydratedoxide of silicon in an amount of 2-10% by weight, preferably 2-5% byweight calculated as SiO₂ as the first layer (the inner layer) and acoating layer of a hydrated oxide of aluminum in an amount of 1-10% byweight, preferably 1-6% by weight calculated as Al₂O₃ as the secondlayer (the outer layer) is used as the titanium dioxide pigmentcontained in the resin composition of the present invention containingan ink resin as a resin component, the resulting resin composition ishigh in opacity, excellent in printability and suitable for reversegravure printing or flexographic printing. As the coating layer ofhydrated oxide of silicon, there may be optionally selected a denselayer, a porous layer, a laminate layer comprising the dense layer andthe porous layer. It is especially preferred to use a titanium dioxidepigment coated with a hydrated oxide of silicon and a hydrated oxide ofaluminum in a total coating amount of 5-15% by weight for flexographicinks. Furthermore, a titanium dioxide pigment coated with no hydratedoxide of silicon and coated with only a hydrated oxide of aluminum in anamount of 5-15% by weight, preferably 5-10% by weight calculated asAl₂O₃ can also be used for flexographic printing inks. When a titaniumdioxide pigment coated with a hydrated oxide of titanium in an amount of0.1-5% by weight, preferably 0.1-2% by weight calculated as TiO₂ inplace of the silicon compound as the first layer (the inner layer) isused, the resin composition is high in gloss and suitable for surfacegravure printing. When a titanium dioxide pigment further coated with apolyhydric alcohol, preferably trimethylolethane or trimethylolpropanein an amount of 0.1-2% by weight, preferably 0.1-1% by weight is used,the affinity between the pigment and the resin component is high and theresin composition can form an ink coating film excellent in surfacesmoothness and gloss.

The ink resin components used can be optionally selected depending onprinting method, kind of the substrate to be printed, and include, forexample, urethane resins, chlorinated vinyl acetate resins, chlorinatedpolypropylene resins, polyamide resins, acrylic resins, maleic acidresins, cyclized rubber resins, pyroxylin, rosin, etc. These ink resincomponents are of organic solvent-dissolving type, water-soluble type,emulsion type, etc., and are not particularly limited. Curing methodsare also not limited, and can be heat-curing type, cold-curing type,ultraviolet-curing type, electron ray-curing type, etc. The resincomposition of the present invention containing the ink resin maycontain organic solvents such as alcohols, esters, ethers, ketones,aromatic hydrocarbons, and aliphatic hydrocarbons, water or mixedsolvents thereof as solvents, and the solvents are selected depending onsuitability for the resin components. In addition, there may becontained various additives, e.g., coloring agents such as organicpigments, inorganic pigments and dyes, extenders, surface active agents,antistatic agents, plasticizers, curing aids, anti-foaming agents,lubricants, antioxidants, ultraviolet absorbers, chelating agents, etc.and fillers depending on the uses.

When an ink resin is used as the resin component, the resin compositionof the present invention is obtained by adding, if necessary, varioussolvents to the titanium dioxide pigment and the ink resin component,followed by dispersing them using a dispersing machine such as sandmill, attritor, disper, ball mill, paint shaker, twin-roll mill, ortriple roll mill. Alternatively, the pigment and the resin component canbe kneaded and made to chips. The above additives and fillers can beadded to the ink during dispersing or after dispersing.

In case the resin composition of the present invention containing aplastic resin is used especially for laminated articles such as waterresistant papers, a peculiar bluish color tone can be imparted due tothe characteristics of anatase type titanium dioxide, namely, highreflectance for light of short wavelength, and in addition, superioropacity can be imparted. Therefore, the pigment concentration can belowered and compositions having substantially no surface defects such aslacing and pin holes can be obtained. Furthermore, the resin compositionof the present invention containing a plastic resin is also useful forthe uses such as injection molded products, extrusion molded products,inflation products and calendered products, and the use is not limitedto laminated products. Moreover, the present invention can be appliednot only to final molded products, but also to intermediate productssuch as color pellets and master batches (color concentrations).

When a titanium dioxide pigment coated with a hydrated oxide of aluminumin an amount of 0.05-2% by weight, preferably 0.1-1.5% by weightcalculated as Al₂O₃ is used as the titanium dioxide pigment contained inthe resin composition of the present invention containing a plasticresin as a resin component, the resulting resin composition is excellentin light resistance and less in content of water originating from theinorganic compound, and hence the composition is suitable for beingprocessed at high temperatures. Moreover, when a titanium dioxidepigment coated with an aluminum phosphate hydrate in an amount of 0.1-2%by weight, preferably 0.5-2% by weight calculated as AlPO₄ in place ofthe aluminum compound is used, the composition is higher in lightresistance. Furthermore, when a titanium dioxide pigment further coatedwith at least one compound selected from a polyhydric alcohol,preferably trimethylolethane or trimethylolpropane, an organosiliconcompound, preferably a polysiloxane or an organosilane, a higher fattyacid preferably stearic acid in an amount of 0.1-2% by weight,preferably 0.1-1% by weight is used, the affinity for the resincomponent is enhanced, and there is obtained a composition excellent insurface appearance with occurrence of substantially no unsatisfactorydispersion of the particles of titanium dioxide pigment. When a titaniumdioxide pigment coated with at least an organosilicon compound or ahigher fatty acid is used, since the surface of the titanium dioxidebecomes hydrophobic, the water absorption is considerably inhibited, anddiscoloration of phenolic antioxidants such as BHT added to the plasticsis also inhibited, and thus more preferred composition is obtained.

The plastic resin component can be optionally selected depending onprocessing method, etc. and there may be used, for example,thermosetting resins such as polyolefin resins, vinyl chloride resins,vinyl acetate resins, polystyrene resins, ABS resins, polyester resins,aromatic resins, nylon resins, polycarbonate resins, cellulose resins,and polylactate resins and thermoplastic resins such as phenolic resins,urethane resins and unsaturated polyester resins, and the plastic resincomponent is not limited. In addition to the titanium dioxide pigmentand the plastic resin component, the resin composition of the presentinvention containing a plastic resin may further contain variousadditives, e.g., coloring agents such as organic pigments, inorganicpigments and dyes, extenders, surface active agents, plasticizers,lubricants, stabilizers, antistatic agents, antioxidants, ultravioletabsorbers, light stabilizers, flame retardants, brightening agents,bactericides, and reinforcing materials, and fillers depending on thepurpose.

In the case of using a plastic resin as the resin component, the resincomposition of the present invention is obtained by adding, ifnecessary, the above additives or fillers to the titanium dioxidepigment and the plastic resin component, and dispersing them by knownmethods using an extrusion molding machine such as single-screw or twinscrew extruder, a roll molding machine such as calender roll, or apressure mixer such as Banbury mixer. Alternatively, the mixture may bepelletized using an extrusion molding machine or a pressure mixer,followed by molding by an injection molding machine or various moldingmachines mentioned above.

EXAMPLES

Examples of the present invention will be given below. These examplesshould not be construed as limiting the invention in any manner.

1. Examples Relating to Titanium Dioxide Pigments and Methods for theProduction of Them.

Example 1

(1) Preparation of Titanium Dioxide Particles:

To hydrous titanium oxide (having a particle diameter of 0.005 μm) wereadded aluminum sulfate corresponding to 0.1% by weight calculated asAl₂O₃, potassium hydroxide corresponding to 0.3% by weight calculated asK₂O and orthophosphoric acid corresponding to 0.15% by weight calculatedas P₂O₅ based on the weight of TiO₂ in the hydrous titanium oxide ascalcination treating agents, and these were calcined by heating at 960°C. for 1 hour using an electric oven to obtain anatase type titaniumdioxide particles. An aqueous slurry of the resulting titanium dioxideparticles having a TiO₂ concentration of 300 g/liter was prepared, andan aqueous sodium hydroxide solution was added thereto to adjust the pHto 10.5 and the particles were dispersed, followed by carrying outgrinding with a sand mill and classification with allowing to stand.

(2) Surface Treatment:

1000 ml of the slurry after subjected to classification was taken, andsulfuric acid was added to the slurry with stirring and with keeping thetemperature at 60° C. to adjust the pH to 9. Then, 40 ml of an aqueoussodium aluminate solution (150 g/liter as Al₂O₃) and sulfuric acid wereadded to the slurry over a period of 20 minutes so as to keep the pH at8-9. Then, pH of the slurry was adjusted to 7 with sulfuric acid,followed by aging for 30 minutes. After the aging, the slurry wasfiltered by a suction filter, washed with water, dried at 120° C. for 20hours, and ground by a jet mill to obtain a titanium dioxide pigment ofthe present invention which had an average particle diameter of 0.25 μmand was coated with an aluminum oxide hydrate in an amount of 2% byweight calculated as Al₂O₃ (Sample A). The sulfate group contained inthe Sample A was in an amount of 0.03% by weight calculated as SO₄.

Example 2

A titanium dioxide pigment of the present invention (Sample B) wasobtained in the same manner as in Example 1, except that the coatingamount of the aluminum oxide hydrate was 0.5% by weight calculated asAl₂O₃.

Example 3

A titanium dioxide pigment of the present invention having an averageparticle diameter of 0.3 μm (Sample C) was obtained in the same manneras in Example 1, except that the amount of potassium hydroxide was 0.32%by weight calculated as K₂O and the amount of orthophosphoric acid was0.08% by weight calculated as P₂O₅ based on the weight of TiO₂ in thehydrous titanium oxide and the calcination was carried out by heating at930° C. for 1 hour.

Example 4

A titanium dioxide pigment of the present invention having an averageparticle diameter of 0.3 μm (Sample D) was obtained in the same manneras in Example 1, except that the amount of potassium hydroxide was 0.36%by weight calculated as K₂O and the amount of orthophosphoric acid was0.04% by weight calculated as P₂O₅ based on the weight of TiO₂ in thehydrous titanium oxide and the calcination was carried out by heating at920° C. for 1 hour.

Example 5

1000 ml of the slurry after subjected to classification in Example 1 wastaken, and 120 ml of an aqueous sodium silicate solution (150 g/liter asSiO₂) was added to the slurry with stirring and with keeping thetemperature at 80° C. over a period of 60 minutes and the pH wasadjusted to 5 with sulfuric acid over a period of 120 minutes, followedby aging for 60 minutes. Then, pH was adjusted to 9 with an aqueoussodium hydroxide solution, and, thereafter, 60 ml of an aqueous sodiumaluminate solution (150 g/liter as Al₂O₃) and sulfuric acid were addedto the slurry over a period of 30 minutes so as to keep the pH at 8-9.Then, pH of the slurry was adjusted to 7 with sulfuric acid, followed byaging for 60 minutes. After the aging, the slurry was washed with water,dried and ground in the same manner as in Example 1 to obtain a titaniumdioxide pigment of the present invention which had an average particlediameter of 0.25 μm and was coated with a silicon oxide hydrate in anamount of 6% by weight calculated as SiO₂ as the first layer and with analuminum oxide hydrate in an amount of 3% by weight calculated as Al₂O₃as the outermost layer (Sample E).

Example 6

1000 ml of the slurry after subjected to classification in Example 1 wastaken, and sulfuric acid was added to the slurry with stirring and withkeeping the temperature at 70° C. to adjust the pH to 3. Then, 60 ml ofan aqueous sodium silicate solution (150 g/liter as SiO₂) was added tothe slurry over a period of 20 minutes and the pH was adjusted to 5 withsulfuric acid over a period of 10 minutes, followed by aging for 30minutes. Then, pH was adjusted to 9 with an aqueous sodium hydroxidesolution, and, thereafter, 60 ml of an aqueous sodium aluminate solution(150 g/liter as Al₂O₃) and sulfuric acid were added to the slurry over aperiod of 30 minutes so as to keep the pH at 8-9. Then, pH of the slurrywas adjusted to 7 with sulfuric acid, followed by aging for 30 minutes.After the aging, the slurry was washed with water, dried and ground inthe same manner as in Example 1 to obtain a titanium dioxide pigment ofthe present invention which had an average particle diameter of 0.25 μmand was coated with a silicon oxide hydrate in an amount of 3% by weightcalculated as SiO₂ as the first layer and with an aluminum oxide hydratein an amount of 3% by weight calculated as Al₂O₃ as the outermost layer(Sample F).

Example 7

1000 ml of the slurry after subjected to classification in Example 1 wastaken, and 80 ml of an aqueous sodium silicate solution (150 g/liter asSiO₂) was added to the slurry with stirring and with keeping thetemperature at 60° C. over a period of 60 minutes, followed by aging for30 minutes. Then, 80 ml of an aqueous sodium aluminate solution (150g/liter as Al₂O₃) was added to the slurry over a period of 40 minutes.Then, pH of the slurry was adjusted to 7 with sulfuric acid over aperiod of 30 minutes, followed by aging for 60 minutes. After the aging,the slurry was washed with water, dried and ground in the same manner asin Example 1 to obtain a titanium dioxide pigment of the presentinvention which had an average particle diameter of 0.25 μm and wascoated with a mixture of a silicon oxide hydrate in an amount of 4% byweight calculated as SiO₂ and an aluminum oxide hydrate in an amount of4% by weight calculated as Al₂O₃ (Sample G)

Comparative Example 1

A titanium dioxide pigment as a comparative sample (Sample H) wasobtained in the same manner as in Example 1, except that the amount ofaluminum sulfate was 0.05% by weight, the amount of potassium hydroxidewas 0.4% by weight and the amount of orthophosphoric acid was 0.4% byweight based on the weight of TiO₂ in the hydrous titanium oxide and thecalcination was carried out by heating at 920° C. for 1 hour. Theresulting titanium dioxide pigment had an average particle diameter of0.16 μm.

Comparative Example 2

A titanium dioxide pigment as a comparative sample (Sample I) wasobtained in the same manner as in Comparative Example 1, except that thecalcination was carried out by heating at 980° C. for 1 hour. Theresulting titanium dioxide pigment had an average particle diameter of0.25 μm.

Comparative Example 3

A titanium dioxide pigment as a comparative sample (Sample J) wasobtained in the same manner as in Example 1, except that the amount ofaluminum sulfate was 0.1% by weight, the amount of potassium hydroxidewas 0.4% by weight and the amount of orthophosphoric acid was 0.8% byweight based on the weight of TiO₂ in the hydrous titanium oxide and thecalcination was carried out by heating at 1010° C. for 1 hour. Theresulting titanium dioxide pigment had an average particle diameter of0.25 μm.

Comparative Example 4

A titanium dioxide pigment as a comparative sample (Sample K) wasobtained in the same manner as in Example 1, except that the amount ofaluminum sulfate was 0.1% by weight, the amount of potassium hydroxidewas 0.3% by weight and the amount of orthophosphoric acid was 0.45% byweight based on the weight of TiO₂ in the hydrous titanium oxide and thecalcination was carried out by heating at 1040° C. for 1 hour. Theresulting titanium dioxide pigment had an average particle diameter of0.3 μm.

Comparative Example 5

A titanium dioxide pigment as a comparative sample (Sample L) wasobtained in the same manner as in Comparative Example 1, except that thecoating amount of the aluminum oxide hydrate was 0.5% by weightcalculated as Al₂O₃.

Comparative Example 6

A titanium dioxide pigment as a comparative sample (Sample M) wasobtained in the same manner as in Example 5, except for using theanatase type titanium dioxide particles obtained in Comparative Example1 and having an average particle diameter of 0.16 μm.

Comparative Example 7

A titanium dioxide pigment as a comparative sample (Sample N) wasobtained using rutile type titanium dioxide particles having an averageparticle diameter of 0.25 μm and carrying out the surface treatment inthe same manner as in Example 1.

Comparative Example 8

A titanium dioxide pigment as a comparative sample (Sample O) wasobtained using the rutile type titanium dioxide particles used inComparative Example 7 and carrying out the surface treatment in the samemanner as in Example 6.

Evaluation 1: Evaluation of Whiteness (Linseed Oil Color):

Whiteness of the samples (A-O) obtained in Examples 1-7 and ComparativeExamples 1-8 was evaluated in accordance with the method of JIS K5116.First, 2.0 g of the sample and 1.25 ml of linseed oil were lightly mixedby a spatula on a glass plate and then kneaded a hand muller byrevolution of 50 times to prepare a paste. The paste was coated on aglass plate using a film applicator of 10 mils. Value L of the coatedpaste in accordance with the Hunter color indication system was measuredby a color difference meter (Z-1001DP manufactured by Nippon DenshokuKogyo Co., Ltd.). The results are shown in Table 1. The samples higherin the L value are superior in whiteness.

Evaluation 2: Measurement of Content of Anatase Type Crystal:

Each of the samples (A-O) obtained in Examples 1-7 and ComparativeExamples 1-8 was packed in an aluminum cell so as to give a smoothsurface, and then content of rutile type crystal (R(%)) was obtainedusing an X-ray diffractometer (RAD-2VC manufactured by Rigaku Co.,Ltd.). The content of anatase type (type A) was 100−R (%). The resultsare shown in Table 1.

Evaluation 3: Evaluation of Particle Size Distribution:

Particle size distribution of the particles of 0.2-0.4 μm in particlediameter was measured on the samples (A-O) obtained in Examples 1-7 andComparative Examples 1-8 from electron photomicrographs using a particleanalyzer (TGZ3 manufactured by Carl Zeiss Co., Ltd.). The particle sizedistribution was based on weight. The results are shown in Table 1.TABLE 1 Surface Average Calcination treating agent treatment Calcinationparticle Content Particle size (%) SiO₂ Al₂O₃ temperature diameterLinseed oil color of distribution Sample Al₂O₃ K₂O P₂O₅ K₂O/P₂O₅ (%) (%)(° C.) (μm) (L value) type A (%) (%) Example 1 A 0.1 0.3 0.15 2/1 0 2960 0.25 96.0 99.6 70 Example 2 B 0.1 0.3 0.15 2/1 0 0.5 960 0.25 96.099.6 70 Example 3 C 0.1 0.32 0.08 4/1 0 2 930 0.3 96.0 98.3 70 Example 4D 0.1 0.36 0.04 9/1 0 2 920 0.3 96.0 98.4 70 Example 5 E 0.1 0.3 0.152/1 6 3 960 0.25 96.0 99.6 70 Example 6 F 0.1 0.3 0.15 2/1 3 3 960 0.2596.0 99.6 70 Example 7 G 0.1 0.3 0.15 2/1 4 4 960 0.25 96.0 99.6 70Comparative H 0.05 0.4 0.4 1/1 0 2 920 0.16 96.0 99.7 10 Example 1Comparative I 0.05 0.4 0.4 1/1 0 2 980 0.25 94.5 99.4 56 Example 2Comparative J 0.1 0.4 0.8 0.5/1   0 2 1010 0.25 94.5 99.7 56 Example 3Comparative K 0.1 0.3 0.45 0.67/1   0 2 1040 0.3 94.9 96.0 56 Example 4Comparative L 0.05 0.4 0.4 1/1 0 0.5 920 0.16 96.0 99.7 10 Example 5Comparative M 0.05 0.4 0.4 1/1 6 3 920 0.16 96.0 99.7 10 Example 6Comparative N — — — — 0 2 — 0.25 96.0 0 81 Example 7 Comparative O — — —3 3 — 0.25 96.0 0 81 Example 82. Examples Relating to Resin Compositions Containing a Paint Resin:

Examples 8-11 and Comparative Examples 9-14

Each of the samples (A-D, H-L and N) obtained in Examples 1-4 andComparative Examples 1-5 and 7 was charged in a glass vessel of 130 ccin volume according to the following formulation 1, followed bydispersing for 20 minutes using a paint conditioner (manufactured by RedDevil Co., Ltd.) to prepare a dispersion. Then, according to thefollowing formulation 2, there was obtained a resin composition (paint)comprising 1 part by weight of the titanium dioxide pigment based on 1part by weight of the resin component and having a solid volumeconcentration of 46%. The respective resin compositions were referred toas samples of Examples 8-11 and Comparative Examples 9-14 (Samples a-j).TABLE 2 Formulation 1 Amount (g) Sample 56.0 Short-oil alkyd resin:BECKOSOL J-524IM 12.8 (manufactured by Dainippon Ink & Chemicals Inc.:Solid content 60 wt %) Xylene 10.24 n-Butanol 2.56 glass beads 60

TABLE 3 Formulation 2 Amount (g) Dispersion of Formulation 1 81.6Short-oil alkyd resin: BECKOSOL J-524IM 52.5 (manufactured by DainipponInk & Chemicals Inc.: Solid content 60 wt %) Butylated melamine resin:SUPER BECKAMINE 28.0 J-820 (manufactured by Dainippon Ink & ChemicalsInc.: Solid content 60 wt %) Xylene 16.88 n-Butanol 4.22Evaluation 4: Evaluation of Opacity, Whiteness and Color Tone:

Each of the resin compositions (paint) (Samples a-j) of Examples 8-11and Comparative Examples 9-14 was coated on a black and white chartpaper using a #30 bar coater, and besides coated on a white chart paperusing a #60 bar coater, and were baked at 110° C. for 40 minutes to formcoating films. Reflectance of the coating film on the black portion andwhite portion on the black and white chart paper (Y_(B) value) and(Y_(W) value), respectively and L value and b value of the coating filmcoated on the white chart paper in terms of Hunter color indicationsystem were measured using a color computer (SM-7 manufactured by SugaTest Instruments Co., Ltd.). The opacity (C_(R) value) was calculated inaccordance with the following formula 1. The results are shown in Table4. The resin composition greater in the C_(R) value was superior inopacity, the resin composition greater in the L value was higher inwhiteness, and the resin composition smaller in the b value was morebluish. The titanium dioxide pigments of the present invention hadnearly the same opacity and whiteness as those of conventional rutiletype titanium dioxide pigments, and had bluish color tone peculiar tothe anatase type.Opacity (C _(R))=(Y _(B) /Y _(W))×100 (%)  Formula 1 TABLE 4 TitaniumColor dioxide Opacity Whiteness tone Sample pigment (C_(R)) (L Value) (bValue) Example 8 a Sample A 89 94 −0.7 Example 9 b Sample B 89 94 −0.7Example 10 c Sample C 89 94 −0.7 Example 11 d Sample D 89 94 −0.7Comparative e Sample H 83 94 −0.9 Example 9 Comparative f Sample I 87 93−0.5 Example 10 Comparative g Sample J 87 92 −0.2 Example 11 Comparativeh Sample K 87 92 −0.1 Example 12 Comparative i Sample L 83 94 −0.9Example 13 Comparative j Sample N 90 94 −0.2 Example 143-1 Examples Relating to Resin Compositions Containing Ink Resin(Solvent Type Gravure Inks):

Examples 12-15 and Comparative Examples 15-18

Each of the titanium dioxide pigments (Samples A, E-G) of Examples 1,5-7 was charged in a glass vessel of 130 cc in volume according to thefollowing formulation 3, followed by dispersing for 30 minutes using apaint conditioner (manufactured by Red Devil Co., Ltd.) to prepare adispersion. Then, according to the following formulation 4, there wasobtained a resin composition (gravure ink composition) of the presentinvention comprising 4 parts by weight of the titanium dioxide pigmentbased on 1 part by weight of the resin component and having a solidvolume concentration of 37.5%. These resin compositions were referred toas samples of Examples 12-15 (Samples k-n). Moreover, gravure inkcompositions were similarly prepared using the titanium dioxide pigments(Samples H, M-O) of Comparative Examples 1, 6-8. These compositions werereferred to as samples of Comparative Examples 15-18 (Samples o-r).TABLE 5 Formulation 3 Amount (g) Sample 50.0 Urethane resin IB-422 50.0(manufactured by Sanyo Kasei Co., Ltd.: Solid content 15 wt %) Glassbeads 100

TABLE 6 Formulation 4 Amount (g) Dispersion of Formulation 3 100.0Urethane resin IB-422 33.3 (manufactured by Sanyo Kasei Co., Ltd.: Solidcontent 15 wt %)3-2 Examples Relating to Resin Compositions Containing Ink Resin(Aqueous Flexographic Inks):

Examples 16-19 and Comparative Examples 19-22

Each of the titanium dioxide pigments (Samples A, E-G) of Examples 1,5-7 was charged in a glass vessel of 130 cc in volume according to thefollowing formulation 5, followed by dispersing for 30 minutes using apaint conditioner (manufactured by Red Devil Co., Ltd.) to prepare adispersion. Then, according to the following formulation 6, there wasobtained a resin composition (aqueous flexographic ink composition) ofthe present invention comprising 6.3 parts by weight of the titaniumdioxide pigment based on 1 part by weight of the resin component andhaving a solid volume concentration of 54.5%. These resin compositionswere referred to as samples of Examples 16-19 (Samples s-v). Moreover,aqueous flexographic ink compositions were similarly prepared using thetitanium dioxide pigments (Samples H, M-O) of Comparative Examples 1,6-8. These compositions were referred to as samples of ComparativeExamples 19-22 (Samples w-z). TABLE 7 Formulation 5 Amount (g) Sample100.0 Aqueous acrylic resin: JONCRYL 501 21.5 (manufactured by JohnsonPolymer Co.: Solid content 29.5 wt %) Pure Water 20.7 Anti-foamingagent: SAN NOPCO 8034 0.7 (manufactured by San Nopco Co.)

TABLE 8 Formulation 6 Amount (g) Dispersion of Formulation 5 142.9Aqueous acrylic resin JONCRYL 501 32.2 (manufactured by Johnson PolymerCo.: Solid content 29.5 wt %) Aqueous wax resin JONWAX 26 8.6(manufactured by Johnson Polymer Co.: Solid content 25 wt %)Evaluation 5: Evaluation of Opacity:

Each of the gravure ink compositions of Examples 12-15 (Samples k-n) andComparative Examples 15-18 (Samples o-r) was diluted with a mixedsolvent of toluene/isopropyl alcohol/methyl ethyl ketone=3/2/5 to a #3Zahn cup viscosity of 15-16 seconds so as to give a practical printingviscosity. The resulting diluted ink was coated on a PET film using a#16 bar coater and subjected to air-drying for 30 minutes to form acoating film. A black chart paper was overlapped on the back surface ofthe PET film (the surface on which the coating film was not formed), andreflectance of the coating film (Y value) and b value according toHunter color indication system were measured using a color computer(SM-7 manufactured by Suga Test Instruments Co., Ltd.). Furthermore,each of the aqueous flexographic ink compositions of Examples 16-19(Samples s-v) and Comparative Examples 19-22 (Samples w-z) was dilutedwith pure water to a #4 Zahn cup viscosity of 7-8 seconds so as to givea practical printing viscosity. The resulting diluted ink was coated ona corrugated board using a #16 bar coater and subjected to air-dryingfor 1 hour to form a coating film. A black chart paper was overlapped onthe back surface of the board, and reflectance of the coating film (Yvalue) and b value according to Hunter color indication system weremeasured using a color computer (SM-7 manufactured by Suga TestInstruments Co., Ltd.). The results are shown in Table 9. Thecompositions higher in reflectance were higher in opacity and thosesmaller in b value had bluish in color tone.

Evaluation 6: Evaluation of Opacity After Lamination:

Each of the gravure ink compositions of Examples 15-18 (Samples o-r) andComparative Examples 19-22 (Samples w-z) was diluted with a mixedsolvent of toluene/isopropyl alcohol/methyl ethyl ketone=3/2/5 to a #3Zahn cup viscosity of 15-16 seconds so as to give a practical printingviscosity. The resulting diluted ink was coated on a PET film using a #4bar coater and subjected to air-drying for 30 minutes to form a coatingfilm, on which an urethane resin (IB-422 having a solid content of 30%by weight manufactured by Sanyo Kasei Co., Ltd.) was coated by a #16 barcoater. Then, an OPP film was superposed on the coating film. Theresulting film was held before a fluorescent lighting, and the degree oftransmission was visually judged to evaluate the opacity afterlamination. The evaluation criteria are as follows.

(Superior) judgement ◯: low transmission of film—judgement X: hightransmission of film (inferior)

Evaluation 7: Evaluation of Abrasion of Metal:

500 g of the diluted ink used in the above evaluation 5 was subjected toan abrasion test with 500,000 revolutions using an abrasion tester (ATII manufactured by Karl Shredder Co., Ltd.). Weight of the test platebefore and after the test was measured and the metal abrasion wasevaluated in terms of the decrement in weight. The ink compositions ofthe present invention showed nearly the same opacity as that ofconventional rutile type titanium dioxide pigments and besides wereexcellent in metal abrasion which is peculiar to the anatase typetitanium dioxide pigments. TABLE 9 Titanium Opacity Metal dioxideOpacity Color tone after abrasion Sample pigment Kind of ink (Y value)(b value) lamination (mg) Example 12 k Sample A Solvent type urethane 71−3.3 ◯ 2.6 resin Example 13 l Sample E Solvent type urethane 73 −3.3 ◯2.8 resin Example 14 m Sample F Solvent type urethane 73 −3.3 ◯ 2.5resin Example 15 n Sample G Solvent type urethane 74 −3.3 ◯ 2.9 resinComparative o Sample H Solvent type urethane 70 −4.0 X 2.4 Example 15resin Comparative p Sample M Solvent type urethane 71 −4.0 X 2.2 Example16 resin Comparative q Sample N Solvent type urethane 71 −3.2 ◯ 6.3Example 17 resin Comparative r Sample O Solvent type urethane 73 −3.2 ◯6.0 Example 18 resin Example 16 s Sample A Aqueous acrylic resin 81 −0.5— 10.5 Example 17 t Sample E ″ 85 −0.3 — 10.0 Example 18 u Sample F ″ 85−0.4 — 11.2 Example 19 v Sample G ″ 85 −0.3 — 10.7 Comparative w SampleH ″ 80 −1.4 — 10.8 Example 19 Comparative x Sample M ″ 83 −1.3 — 10.2Example 20 Comparative y Sample N ″ 82 −0.4 — 21.7 Example 21Comparative z Sample O ″ 86 −0.3 — 21.2 Example 224. Examples Relating to Resin Compositions Containing Plastic Resin:

Example 20 and Comparative Example 23

A mixture of the following formulation 7 was prepared using the titaniumdioxide pigment (Sample B) of Example 2. This mixture was heated andmolten using a twin-screw extruder (Labo Plastmill manufactured by ToyoSeiki Mfg. Co., Ltd.; L/D=25, D=20 mmφ) so that the resin temperaturereached 280° C., followed by kneading over a period of 1 hour andmolding the kneaded product into a film of 50 μm in thickness by a T-dieto obtain a resin composition (plastics resin composition) of thepresent invention containing 1 part by weight of the titanium dioxidepigment for 1 part by weight of the resin component. This was referredto as a sample of Example 20 (Sample-a′). The extrusion opening of thetwin-screw extruder was fitted with a screen of 1450 mesh. A plasticsresin composition was similarly prepared using the titanium dioxidepigment of Comparative Example 5 (Sample L). This was referred to as asample of Comparative Example 23 (Sample b′). TABLE 10 Formulation 7Amount (g) Sample 500 Polyethylene resin SUMIKASEN L-705 500(manufactured by Sumitomo Chemical Co., Ltd. Frozen ground material)Zinc stearate 20Evaluation 8: Evaluation of Opacity:

Transmission (T value) of the polyethylene films of Example 20 andComparative Example 23 (Samples a′ and b′) for visible light of 440 nm,540 nm and 640 nm in wavelength was measured using a spectrophotometer(UV-2200A manufactured by Shimadzu Seisakusho Ltd.). The results areshown in Table 11. The films smaller in T value were superior inopacity.

Evaluation 9: Evaluation of Dispersibility:

In molding the polyethylene films of Example 20 and Comparative Example23 (Samples a′ and b′) into polyethylene films, resin pressures at theextrusion opening of the extruder before and after kneading weremeasured. The results are shown in Table 11. Those which were smaller inthe difference of the pressure (Δ P) were superior in dispersibility.The plastics resin compositions of the present invention were not onlysuperior in opacity, but also superior in dispersibility to thosecomprising conventional anatase type titanium dioxide pigments. TABLE 11Titanium Opacity Dispersibility Sam- dioxide T(%) ΔP ple pigment 440 nm540 nm 640 nm (kg/cm²) Exam- a′ Sample B 8.0 11.1 14.9 10 ple 20 compar-b′ Sample L 8.6 12.1 15.6 50 ative Exam- ple 23

INDUSTRIAL APPLICABILITY

The titanium dioxide pigment of the present invention hascharacteristics peculiar to anatase type, for example, opticalcharacteristics such as bluish color tone and physical characteristicssuch as low hardness, and furthermore has high opacity not possessed bythe conventional anatase type titanium oxide pigments, and hence isuseful in various resin compositions, particularly, those which containresins for paints, inks, plastics or the like.

1. A titanium dioxide pigment containing an anatase type crystal in anamount of 98-100% and having an average particle diameter in the rangeof 0.2-0.4 μm and a whiteness in the range of 95-97 in terms of L valueof linseed oil.
 2. A titanium dioxide pigment according to claim 1 whichcontains 50-100% by weight of particles having a particle diameter inthe range of 0.2-0.4 μm.
 3. A titanium dioxide pigment according toclaim 1 in which content of sulfate group is not more than 0.1% byweight calculated as SO₄.
 4. A titanium dioxide pigment according toclaim 1, the surface of which is coated with at least one compoundselected from an inorganic compound and an organic compound.
 5. Atitanium dioxide pigment according to claim 4, wherein the inorganiccompound is at least one compound selected from aluminum compound,silicon compound, zirconium compound, tin compound, titanium compoundand antimony compound.
 6. A titanium dioxide pigment according to claim5, wherein the inorganic compound is at least one compound selected fromoxide, hydrated oxide, hydroxide and phosphate salt.
 7. A titaniumdioxide pigment according to claim 6, wherein the coating amount of eachinorganic compound is in the range of 0.05-15% by weight.
 8. A titaniumdioxide pigment according to claim 4, wherein the organic compound is atleast one compound selected from polyhydric alcohol, alkanolamine orderivative thereof, organosilicon compound, and higher fatty acid ormetal salt thereof.
 9. A titanium dioxide pigment according to claim 8,wherein the total coating amount of the organic compound is in the rangeof 0.01-5% by weight.
 10. A method for producing an anatase typetitanium dioxide pigment by calcination of a hydrous titanium oxide withheating in the presence of a calcination treating agent, the methodcomprises calcining the hydrous titanium oxide by heating it at atemperature of not lower than 800° C. and lower than 1000° C., using asthe calcination treating agents an aluminum compound corresponding to0.02-0.2% by weight calculated as Al₂O₃, a potassium compoundcorresponding to 0.2-1% by weight calculated as K₂O and a phosphoricacid compound corresponding to 0.02-0.5% by weight calculated as P₂O₅based on the weight of TiO₂ in the hydrous titanium oxide, the ratioK₂O/P₂O₅ being in the range of 1.5/1-10/1.
 11. A method for producing atitanium dioxide pigment according to claim 10, wherein the hydroustitanium oxide has a particle diameter of 0.001-0.01 μm.
 12. A resincomposition comprising a titanium dioxide pigment and a resin componentwherein the titanium dioxide pigment contains an antase type crystal inan amount of 98-100%, has an average particle diameter in the range of0.2-0.4 μm and has a whiteness in the range of 95-97 in terms of L valueof linseed oil.
 13. A resin composition according to claim 12, whereinthe titanium dioxide pigment contains 50-100% by weight of particleshaving a particle diameter in the range of 0.2-0.4 μm.
 14. A resincomposition according to claim 12, wherein the resin component is apaint resin, an ink resin or a plastic resin.
 15. A resin compositionaccording to claim 12 which contains the titanium dioxide pigment in anamount of 0.5-10 parts by weight based on 1 part by weight of the paintresin component.
 16. A resin composition according to claim 12 whichcontains the titanium dioxide pigment in an amount of 0.5-10 parts byweight based on 1 part by weight of the ink resin component.
 17. A resincomposition according to claim 12 which contains the titanium dioxidepigment in an amount of 0.05-2 parts by weight based on 1 part by weightof the plastic resin component.